Groundwater Quality

Groundwater
quality describes the condition of groundwater relative to substances that are dissolved or suspended
in the water. Suspended material is not transported far in most
subsurface materials, but it is usually filtered (blocked by
pore-size or by adhesion to aquifer material) as the water
circulates through small openings in the soil or bedrock. In
general, groundwater flow is very slow and depends on the
permeability (water transmitting properties) of the subsurface
materials, as wells as the hydraulic gradient (slope of the
water-table or pressure gradient for artesian conditions). The
rate of groundwater flow is usually
measured in feet (or meters) per day or feet (or meters) per year.
In some situations where flow is very slow it is measured in inches (or
centimeters) per year. Groundwater usually contains higher
concentrations of natural dissolved
materials than surface water. The materials dissolved in the water
usually reflect the composition and solubility of the earth
materials (soil or rock) that the groundwater is in contact with and
time that it has been in the subsurface. A number of the
activities of man pose threats to water quality. Some of these
activities include:

Landfill solid waste disposal

Liquid waste disposal

Septic waste infiltration systems

Highway deicing with chemicals (e.g. salt)

Gasoline service stations

Petroleum bulk storage facilities

Underground storage tanks

Many industrial activities

Livestock feed lots

Urban stormwater infiltration

The illustration above presents an example of how a
source of groundwater contamination can pollute millions of gallons
of groundwater in an underlying aquifer. The "industrial area" is
presented as a typical source of contamination. In the
illustration, the groundwater contaminants are volatile organic
chemicals (e.g. trichloroethene or TCE) that are used as solvents or
degreasers in various industrial processes. The degree of
contamination is indicated by the concentration of total volatile
organics by contours. Degree of contamination is also illustrated
by varying colors in the aquifer. Those closest to the industrial
area have the highest concentrations, while those at a distance or
upgradient have lower concentrations. The downgradient water
supply well is being impacted by the contamination from the
industrial area and may have to be shut down until the aquifer is
remediated (cleaned up).

The groundwater properties of
temperature and conductivity can be used to rapidly delineate bodies
of varying water quality. The quality of water in
wells and boreholes
that penetrate the groundwater may be characterized by a new
instrument by Heron Instruments called the
Conductivity
Plus. It is a combination conductivity (or specific
conductance), temperature, and water level meter.
It comes in lengths from 100 feet (or 30 m) to 1,000 feet (or 300 m)
in length.